The present invention relates to a memory fine tuning arrangement used for television tuners. More particularly, the invention relates to a television tuner of the type which provides a so-called pre-setting fine tuning arrangement for an automatic fine tuning adjustment for each individual television channel. Specifically, the present invention is directed to an improved and simplified fine tuning mechanism used for rotary pre-setting fine tuning devices and which is manufactured economically by a minimum number of parts.
Generally, mechanical channel selecting devices for VHF television tuners are mainly classified as rotary-switching types or turret types. Turret type tuners include an incrementally rotatable channel selector shaft for selectively connecting certain ones of a plurality of tuned circuit elements for each of a plurality of channel selector positions. For example, one such turret tuner arrangement is disclosed in U.S. Pat. No. 4,128,821, wherein a rotatable turret having a plurality of tuning coil units, is rotatably mounted on a chassis base.
For clear reception in each of the channel positions of the selector shaft, it is customary to include in the local oscillator circuit an adjustable impedance device. This impedance device is conventionally adjusted by means of a fine tuning shaft concentrically mounted with respect to the channel selector shaft. The fine tuning shaft is connectable by the viewer or user to adjust the tuning impedance for each predetermined position of the selector shaft. Various memory fine tuning arrangments have been proposed to maintain individual channel tuning arrangements once they have been established by the user or operator without requiring any adjustment of the fine tuning shaft of the tuner by the user each time a particular channel is selected. One such arrangement is the push pre-setting type fine tuning device which requires the operator to push in a control knob of the fine tuning shaft while maintaining pressure on the knob to rotate the same to adjust a fine tuning element within the tuner. The other arrangement is a rotary pre-setting type fine tuning device which requires the operator to only rotate a control knob of the fine tuning shaft for fine tuning adjustment. These devices are particularly useful on turret type television tuners having tuned coil assemblies or units for each channel. These coil units are removably mounted in the rotatable turret structure, and are provided individually with an oscillator coil, the inductance of which may be adjusted by means of an adjustable element which extends into an opening in the end of the coil units adjacent the oscillator coil.
Since television tuners are made in large volumes, in order to be commercially competitive, it is desirable to provide a low cost pre-setting fine tuning device with a minimum number of parts which may be assembled in an easy and simple manner. The fine tuning device requires a mechanical arrangement for translation of rotary motion of the fine tuning shaft into rotary motion of the adjustment element, since the fine tuning shaft is offset laterally from the axis of the adjustment element in the individual coil units. Further, engagement of the fine tuning shaft with the adjustment element must terminate automatically when the user releases the fine tuning shaft so that the turret is free to rotate to another channel position. For example, such fine tuning devices are disclosed in U.S. Pat. Nos. 3,316,770; 3,466,549; 4,041,422; 4,128,821; and 4,152,682 for push pre-setting type memory fine tuners, and in U.S. Pat. Nos. 3,183,726 and 3,898,879 for rotary pre-setting type memory fine tuners. U.S. Pat. No. 4,172,390; granted on Oct. 30, 1979, discloses a fine tuning device including a pivotally mounted member on the front wall of the chassis base with a coil spring between the member and the front wall to exert a bias force on the member in a predetermined direction. It has been found that the number of parts of such fine tuning devices may be still further reduced thereby decreasing the manufacturing costs and making the assembly easier.